1. Terminology
A colloidal system, which consists of very finely divided liquid or solid particles dispersed in and surrounded by a gas, is called an "aerosol" when sprayed or dispensed into the atmosphere. The term "aerosol" is also used for the dispensers from which the liquid or solid particles are sprayed, propelled by a gas as a colloidal system, into the atmosphere. The term "aerosol" is to be used herein also to means gas, with or without dispersed products, sprayed into the atmosphere or dispsned from a container in accordance with a pressure differential.
2. Prior Art
It has been reported that the first U.S. patent for an aerosol dispenser was issued on Oct. 5, 1943, as U.S. Pat. No. 2,331,117 to L. D. Goodhue et al. The Goodhue et al. patent discloses a refillable dispenser designed to dispense a metered dose of a liquid product, which, when the dispenser is tipped, is held in a pocket from which a tube extends to a nozzle having a screw type operating valve. The liquid product contains a component volatile at ordinary room temperatures so as to produce a gas under sufficient pressure to expel the liquid from the pocket, through the tube, through the nozzle, and into the atmosphere when the valve is open. Goodhue et al. suggested components like dichlorodifluoromethane, carbon dioxide, and methylbromide. The expelled gas atmozies into the atmosphere.
3. Development of Technology
The technology of aerosol dispensing has moved forward since Goodhue et al., with advances in valve arrangements, propellants, and techniques for dispensing a wide variety of products such as hair spray, foam cleanser, toothpaste, and lacquer. The valve of a dispenser is now normally held shut by a coil spring directly below a valve stem and by the pressure within the product containing chamber of the dispenser. With this arrangement, a push button nozzle on the end of the valve stem may be pressed to force the valve stem down in its housing and to uncover a small passageway leading through the stem to the nozzle. The product is forced out through the passageway into the atmosphere.
Many propellants are now available for use with aerosols, propellants such as chlorinated hydrocarbons, propane, butane, vinyl chloride, and nitrogen. In addition to the two phase system disclosed in Goodhue et al., in which the propellant gas and the product to be discharged are separate layers within the dispenser, dispensers now contain the product to be dispensed and the propellant gas as a solution. The solution is developed by dissolving the product to be dispensed as an aerosol in alcohol so as to make it completely miscible with a liquid propellant. When the solution is exposed to the atmosphere, the propellant vaporizes to pressurize the dispenser chamber in which the liquid is contained, so as to force the liquid out of the dispenser into the atmosphere.
Different techniques are now used to produce different consistencies of aerosols. For example, to produce a fine mist, a propellant miscible with the product is used so that, as the solution leaves the nozzle, the propellant vaporizes to produce colloids of the product. By using a viscous solution and a relatively wide nozzle, a foam is produced. When a non-mixing product is forced through the tube by the pressure of the propellant within the chamber, a continuous stream of the product is produced.